Method of manufacturing electrical cable, and resulting product, with reduced required installation pulling force

ABSTRACT

Disclosed is type THHN cable having a reduced surface coefficient of friction, and the method of manufacture thereof, in which the central conductor core and insulating layer are surrounded by a nylon sheath. A high viscosity, high molecular weight silicone based pulling lubricant for THHN cable, or alternatively, erucamide or stearyl erucamide for small THHN gauge wire, is incorporated, by alternate methods, with the nylon material from which the outer sheath is extruded, and is effective to reduce the required pulling force on the cable during installation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/787,877,filed May 26, 2010, now pending, which is a continuation of applicationSer. No. 11/675,441, filed Feb. 15, 2007, now U.S. Pat. No. 7,749,024,issued Jul. 6, 2010, which is a continuation-in-part of application Ser.No. 11/120,487, filed May 3, 2005, now abandoned, which is acontinuation-in-part of application Ser. No. 10/952,294, filed Sep. 28,2004, now U.S. Pat. No. 7,411,129, issued Aug. 12, 2008. Each patentapplication identified above is incorporated here by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to electrical cables, more particularly toTHHN electrical cables, and even more particularly to methods forreducing the surface coefficient of friction and required installationpulling force thereof, as well as preferred pulling lubricantcompositions for effecting such reductions.

BACKGROUND OF THE INVENTION

Electrical cables include a conductor core and typically include anouter jacket or sheath. The term “sheath,” as used herein and throughoutthe specification and claims, is defined to mean the outermostprotective jacket or covering surrounding a conductor core, whether of asingle type material or multiple layers of the same or differentmaterial. The conductor core may typically be, for example, a singlemetal wire, multiple small wires twisted together to make a “stranded”cable, or multiple insulated wires or other type electrical conductorsacting together to serve a particular function (e.g., three-phaseconnection). The sheath may comprise one or more layers of polymeric orother material to provide physical, mechanical, electrical insulatingand/or chemical protection for the underlying cable components. For thepurpose of type THHN cable of the present invention, the exteriorportion of the sheath is of nylon. Specifically, type THHN cablecomprises a conductor core of a single solid or stranded conductor,surrounded by a layer of polyvinyl chloride (PVC) electrical insulation,covered by an outer layer of nylon.

Installation of electrical cable often requires that it be pulledthrough tight spaces or small openings in, and in engagement with,narrow conduits, raceways, cabletrays, or passageways in rafters orjoists. This becomes problematic since the exterior surface of the cablesheath normally has a high coefficient of friction, therefore requiringa large pulling force. Moreover, installation parameters include maximumallowable cable pulling tension and/or sidewall pressure limits.Exceeding these limits can result in degradation of the cable, physicaldamage and inferior installation.

To overcome this problem, the general industry practice has been to coatthe exterior surface of the cable sheath with a pulling lubricant at thejob site in order to reduce the coefficient of friction between thissurface and the conduit walls or like surfaces, typically usingvaselines or lubricants produced specifically, and well known in theindustry for such purpose, such as Yellow 77® (hereinafter, “Y 77”). Theterm “pulling lubricant,” as used herein and throughout thespecification and claims, is defined to mean lubricating material whichsufficiently reduces the coefficient of friction of the exterior surfaceof the sheath of the cable to facilitate the pulling of the cable.

The aforementioned industry practice of applying a pulling lubricantlike Y 77 to the finished cable at the job site poses problems,principally due to the additional time, expense and manpower required tolubricate the finished cable surface at the job site as well as to cleanup after the lubricating process is completed. Alternative solutionshave been tried but are generally unsuccessful, including the extrusionof a lubricant layer over the extruded polymeric sheath during themanufacturing of the cable, or the application of granules of materialto the still-hot sheath during the extrusion process, which granules aredesigned to become detached when the cable is pulled through the duct.However, these solutions not only require major alterations of themanufacturing line, but result in a loss in manufacturing time,increased economic costs, and undesirable fluctuations in thegeometrical dimensions of the cable sheaths.

It is also important to an understanding of the present invention toknow the difference between what are referred to as “pulling lubricants”and what are “processing lubricants.” A pulling lubricant is a lubricantthat appears at the outside surface of the sheath of the cable and iseffective to lower the surface coefficient of friction such as to reducethe force necessary to pull the cable along or through building surfacesor enclosures. A processing lubricant is lubricating material that isused to facilitate the cable manufacturing process, such as the flow ofpolymer chains during any polymer compounding as well as during theextrusion processes while the polymer is in its molten or melt phase.Cable manufacturers have long used processing lubricants, such asstearic acid or ethylene bis-stearamide wax, as a minor component of thepolymeric compound from which the cable sheath is formed. Because aprocessing lubricant is normally not effective except when the polymeris in this melt phase, the effect of a processing lubricant isessentially non-existent in the final hardened polymer sheath of thecable. Even where there may be an excessive amount of the processinglubricant, a separate pulling lubricant would still be required tosufficiently reduce the cable sheaths' exterior surface coefficient offriction in order to minimize the pulling force necessary to install thecable.

Accordingly, there has been a long-felt need for an effective method ofproviding a pulling lubricant at the exterior surface of the finishedcable, and particularly the finished THHN cable, which is effective toreduce the cable surface coefficient of friction and minimize therequired installation pulling force, without incurring the inconvenienceand time-consuming operation and expense associated with the applicationof the pulling lubricant at the installation site, nor significantlyincreasing the complexity and cost of the manufacturing process, norundesirably altering the geometrical characteristics of the cablesheaths.

SUMMARY OF THE INVENTION

The process of the present invention accomplishes these objectives forTHHN cable by a cable manufacturing process in which a particularpulling lubricant, of optimum weight percentage or quantity, isintroduced into the manufacturing process at a particular stage ofmanufacture, which results in the pulling lubricant being present in theouter sheath, so that it is available to reduce the coefficient offriction of the exterior sheath surface when the cable is to beinstalled. Depending upon the material of the sheath and the type oflubricant, this may be as a consequence of the migration, or delayedmigration or “blooming,” of the pulling lubricant to the sheath surface;or alternatively, due to the permeation of the pulling lubricantthroughout the sheath. Under these circumstances, the pulling lubricantis effective to lower the surface coefficient of friction below that ofthe inherent coefficient of friction of the material from which theouter layer of the THHN sheath is formed, thereby reducing the requiredinstallation pulling force.

In accordance with the process of the invention, and as described belowin greater detail, the pulling lubricant is selectively chosen toprovide the optimum results with respect to the particular nylon sheathmaterial, and may alternately be introduced into the THHN cablemanufacturing process at various stages, ranging from the initialcompounding of the lubricant with the polymeric nylon material to formlubricated pellets from which the sheath is to be formed, to mixing thelubricant with the nylon sheath material before introduction of themixture into the extrusion process, to its introduction into the sheathextrusion process while the nylon sheath forming material is in itsmolten state.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other details and aspects of the invention, as well as theadvantages thereof, will be more readily understood and appreciated bythose skilled in the art from the following detailed description, takenin conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of typical equipment used in themanufacture of cable in accordance with the present invention, whenmixing the lubricant with the nylon material prior to extrusion;

FIG. 2 is a graphical representation of test data comparing the effectof different pulling lubricants in small size THHN cable in which theouter sheath material is nylon;

FIG. 3 is a graphical representation of test data comparing both theeffects of different pulling lubricants and different percentages ofpulling lubricant in large size THHN cable in which the outer sheathmaterial is nylon;

FIGS. 4 and 5 are representations of test devices which may be used tocreate the aforementioned test data; and

FIG. 6 is a section view of a THHN cable produced in accordance with theprocess of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring initially to FIG. 1, there is depicted typical equipment 11for manufacturing electrical cable 12 in accordance with one process ofthe present invention. The outer sheath of the cable is of an extrudedpolymer material, specifically nylon. The equipment 11 may include areel 13 which supplies conductor wire 14 to an extruding head 15. Inflow communication with the extrusion head is a tank 16 of the nylonpellets 17. A tank 18 with the desired pulling lubricant 19 is adaptedto be in flow communication with the tank 16 by way of conduit 22, thusenabling the mixing of the pulling lubricant with the nylon pellets 17,the mixture thereafter introduced into the extruder. Alternatively, thetank may be adapted to be in fluid communication with the extruder orextrusion head 15, by way of conduit 23, downstream from the point ofentry of the nylon material, thus allowing the pulling lubricant to mixwith the nylon material while in its molten state in the extruder orextruder head. A cooling box 20 for cooling the extruded product isprovided, and a reel 21 is positioned for taking up the resulting cableassembly 12. When the final cable construction is such that there aremultiple layers of sheath material, the pulling lubricant shoulddesirably be incorporated into the outermost layer.

As is therefore evident, the pulling lubricant can be mixed with thematerial from which the outer sheath is to be extruded prior toextrusion or, alternatively, introduced into the extruding head forsubsequent mixing with the molten extrusion material as the sheath isbeing formed. As a further alternative, the pulling lubricant can beinitially compounded with the polymeric material of the pelletsthemselves in a process upstream of that depicted in FIG. 1, therebyforming lubricated polymeric pellets, thus eliminating the need for tank18 and conduits 22 and 23.

Polymeric materials that can be used for an insulating layer or outersheath of different type of cable include polyethylene, polypropylene,polyvinylchloride, organic polymeric thermosetting and thermoplasticresins and elastomers, polyolefins, copolymers, vinyls, olefin-vinylcopolymers, polyamides, acrylics, polyesters, fluorocarbons, and thelike. As previously described, for the THHN cable of the presentinvention, the conductor core of a single solid or stranded conductor issurrounded by an insulating layer of PVC covered by an outer sheath of apolyamide (e.g., nylon).

In accordance with the testing subsequently described, it has beendetermined that, for THHN cable, silicone oil is the preferred pullinglubricant. For small gauge THHN wire, erucamide is an alternativepreferred pulling lubricant, to be incorporated in the nylon sheath.

The efficacy of these pulling lubricants for the nylon sheath, andspecifically an optimum range for the quantity of such lubricants, inaccordance with the invention, has been proven by the use of varioustests. Prior to discussing the results of such tests, these test methodsand their equipment are described as follows:

Testing Method

Coefficient of Friction Test

Referring now to FIG. 4, diagrammatically illustrated is the apparatusfor a coefficient of friction test. The coefficient of friction testapparatus was developed to give a consistent way to determine the inputvalues necessary to use the industry-standard program published byPolyWater Corporation to calculate a real-world coefficient of frictionfor a given cable being pulled in conduit. Given the inputs for theconduit setup, the back tension on the wire, and the pulling tension onthe pulling rope, this program back-calculated a coefficient of frictionfor the cable by subtracting the back tension from the pulling tensionand attributing the remaining tension on the rope to frictional forcesbetween the cable and the conduit.

The overall setup used a pulling rope threaded through ˜40′ of PVCconduit (appropriately sized for the cable being pulled) with two 90°bends. Three 100′ pieces of THHN cable were cut and laid out parallel toone another in line with the first straight section of conduit, and therope connected to them using industry-standard practice. The other endof the THHN cable was attached to a metal cable which was wrapped arounda cylinder with an air brake to allow the application of constant backtension on the setup.

The metal cable was threaded through a load cell so that it could bemonitored in real-time, and continuously logged. The pulling rope wassimilarly threaded through a load cell and constantly monitored andlogged. Values for both back tension and pulling tension were logged forthe time it took to pull cable through the conduit run. These valueswere then averaged and used in the PolyWater program to calculatecoefficient of friction.

Specific Type THHN Tests

Initial tests of small gauge Type THHN wire were performed using thesmall-scale tension tester shown in FIG. 5. In this test, multipleindividual American Wire Gauge (AWG) size 12 THHN wires were provided onthe payoff and attached to a metal pulling tape that was threadedthrough an arrangement of ½″ conduit that included about 50 feet ofstraight conduit and four 90° bends. A pulling rope was attached to theother end of the pulling tape and a tugger was used to pull the cablearrangement through the conduit. The rope was threaded through a pulleyarrangement that used a load cell to monitor rope tension while the wirewas pulled through the conduit. This tension was continuously logged andaveraged to give an average pulling force for the pull. This forcecorrelated directly to the coefficient of friction for the cable.

Using the data obtained from the small scale pull test of FIG. 5, FIG. 2illustrates a comparison of the different required pulling forces for asmall gauge cable consisting of multiple (AWG) size 12 THHN conductors.The test subjects had 0.25-0.85% of two different potential pullinglubricants, erucamide and stearyl erucamide, mixed into the outer nylonsheath. Results of the test are shown in FIG. 2 and compared to theresults for the standard THHN product without any pulling lubricant andwith the externally applied industry-standard Y77. This test shows thaterucamide is one preferred lubricant for small gauge THHN cable, in anoptimum percentage of approximately 0.85%, by weight.

Next, large gauge Type THHN cable was tested. Using the coefficient offriction test of FIG. 4, FIG. 3 illustrates the different values ofsurface coefficient of friction of the exterior surface of the sheath,for cables consisting of three individual large gauge AWG 4/0 THHNconductors, for varying percentages of the pulling lubricant, siliconeoil, of varying molecular weights. The two lubricants compared in FIG. 3are a high-molecular weight silicone oil (HMW Si) and a lower molecularweight silicone oil (LMW Si). Comparison results are shown for this sameTHHN cable arrangement lubricated with industry-standard Y77, as well aswith respect to three other trial pulling lubricants, fluorinated oil,molydisulfide, and stearyl erucamide. The results in FIG. 3 illustratethat, while other pulling lubricants can reduce the coefficient offriction of the exterior surface of the cable, the preferred pullinglubricant for THHN cable, and particularly large gauge THHN cable, is ahigh molecular weight silicone oil added at a level of approximately 9%,by weight, or higher.

In accordance with an advantage of the present invention, the pullinglubricant that is incorporated in the sheath is present at the outersurface of the sheath when the cable engages, or in response to thecable's engagement with, the duct or other structure through which thecable is to be pulled. For the THHN cable of the present invention,where the outer sheath is of nylon and the preferred pulling lubricantis high molecular weight silicone oil, this silicon-based lubricantpermeates the entire nylon sheath portion and is, in effect,continuously squeezed to the sheath surface in what is referred to asthe “sponge effect,” when the cable is pulled through the duct.

Compounding with Pulling Lubricant

As previously described, the pulling lubricant may be incorporated intothe extruded sheath (or the outer layer of the cable sheath if thesheath is of multiple layers) by initially compounding the lubricantwith the (outer) sheath material to be extruded. To prepare thelubricated blend of the present invention, the resin and additionalcomponents, including the pulling lubricant, are fed into any one of anumber of commonly used compounding machines, such as a twin-screwcompounding extruder, Buss kneader, Banbury mixer, two-roll mill, orother heated shear-type mixer. The melted, homogeneous blend is thenextruded into strands or cut into strips that may be subsequentlychopped into easily handled pellets. The so-prepared lubricated pelletsare then fed into the extruder for forming the outer sheath.

THHN cable

THHN and THWN-2 are types of insulated electrical conductors that covera broad range of wire sizes and applications. THHN or THWN-2 conductorsare typically 600 volt copper conductors with a sheath comprising anouter layer of nylon surrounding a layer of thermoplastic insulation andare heat, moisture, oil, and gasoline resistant. THHN cable is primarilyused in conduit and cable trays for services, feeders, and branchcircuits in commercial or industrial applications as specified in theNational Electrical Code and is suitable for use in dry locations attemperatures not to exceed 90° C. Type THWN-2 cable is suitable for usein wet or dry locations at temperatures not to exceed 90° C. or not toexceed 75° C. when exposed to oil or coolant. Type THHN or THWN-2conductors are usually annealed (soft) copper, insulated with a tough,heat and moisture resistant polyvinylchloride (PVC), over which apolyamide layer, specifically nylon, is applied. Many cables, includingthose addressed by the present invention, can be “multi-rated,”simultaneously qualifying for rating as THHN or THWN-2.

Referring now to FIG. 6, there is illustrated a THHN cable 24constructed in accordance with the process of the invention. The cableis characterized by a sheath comprising an extruded layer 25 of PVCinsulation material and an overlying extruded thin layer 26 of nylon,the sheath surrounding a central electric conductor 27 which is usually,though not exclusively, of copper. The only limitation on the type ofpulling lubricant to be incorporated into the extruded outer nylonsheath is that it be sufficiently compatible with nylon to beco-processed with it, and particularly when compounded with nylon, thatit be robust enough to withstand the high processing temperature fornylon, which is typically about 500° F. However, it has been found thatfor THHN cable, this lubricant is preferably a high molecular weight,high viscosity silicone fluid; for small gauge THHN wire, as analternative, erucamide or stearyl erucamide.

Two industry-standard processes can be used to produce this product, theso called co-extrusion method and the tandem extrusion method. In bothprocesses, the conductor, either solid or stranded, is first introducedinto the extrusion head where the heated, melted PVC insulation compoundis introduced and applied to the circumference of the conductor. In theco-extrusion process, the melted nylon compound is introduced into thesame extrusion head and applied together with the PVC to the conductor,in a two-layer orientation. In the tandem process the PVC-coatedconductor leaves the first extrusion head and is introduced into asecond, separate extrusion head where the melted nylon is applied to thesurface. In both cases, the final product is then introduced into acooling water bath and ultimately the cooled product is wound ontoreels. In either case, the nylon material is preferably initiallycompounded with the pulling lubricant to provide the so-lubricatedextrusion pellets.

As shown in FIG. 2, small gauge THHN cable prepared, as described, withnylon as the outer layer of the sheath, and containing 0.25%, 0.50% and0.85%, by weight, of stearyl erucamide, had an average pulling force of18.1 lbs, 16 lbs and 18.5 lbs, respectively. Even better, small gaugeTHHN cable containing 0.25%, 0.50% and 0.85%, by weight, of erucamidehad an average pulling force of 13.2 lbs, 10.3 lbs and 9.6 lbs,respectively. Comparably, the pulling force for a THHN cable with nopulling lubricant was measured at 38.5 lbs, and THHN cable with only Y77 applied to the exterior surface was measured at 15.3 lbs. FIG. 3, onthe other hand, illustrates the results when silicone oil is used inTHHN cable, compared to other potential lubricants, illustratingsilicone oil as a much preferred pulling lubricant for this type cable.

Although the aforementioned description references specific embodimentsand processing techniques of the invention, it is to be understood thatthese are only illustrative. For example, although the description hasbeen with respect to electrical cable, it is also applicable to othertypes of non-electrical cable such as, for example, fiber optic cable.Additional modifications may be made to the described embodiments andtechniques without departing from the spirit and the scope of theinvention as defined solely by the appended claims.

1. In a power cable of the type comprising a conductor and sheathsurrounding said conductor, in which the sheath has at least itsexterior portion formed of nylon material, an improvement in which aerucamide pulling lubricant is introduced in said material during themanufacture of the cable, and either permeates throughout, or migratesthrough, at least said exterior portion of the sheath to be available atthe exterior surface of said sheath as said power cable is pulled alongan installation surface through building passageways in rafters orjoists or conduit bends, and in a concentration sufficient to reduce therequired installation pulling force for installation of the cablethrough building passageways in rafters or joists or conduit bends. 2.The improvement as defined by claim 1 in which the pulling lubricant iserucamide in a concentration, by weight, of approximately 0.85%.
 3. Theimprovement as defined by claim 1 in which the pulling lubricant iserucamide in a concentration, by weight, of between about 0.25% and0.85%.
 4. The improvement as defined by claim 1 in which the requiredinstallation pulling force is measured by a test apparatus and is lessthan the required installation pulling force to pull a power cable ofthe same type and size having only externally applied lubricant throughsaid test apparatus, the test apparatus (i) constructed of a PVC conduitthat is sized to accommodate said power cable and (ii) comprising afirst conduit segment of about 10 feet separated from a second conduitsegment of about 30 feet by two 90° bends, the second conduit segmentseparated from a third conduit segment of about 5 feet by a 90° bend,and the third conduit segment separated from a fourth conduit segment ofabout 10 feet by another 90° bend.
 5. The improvement as defined byclaim 4, wherein the externally applied lubricant is one of thefollowing fluorinated oil, moly disulfide, and Y77.
 6. The improvementas defined by claim 1, wherein the required installation pulling forceis a quantifiable reduction of at least about 50% in comparison to therequired installation pulling force of a non-lubricated cable of thesame cable type and size through an arrangement of conduit, thearrangement of conduit being defined as PVC conduit that is sized toaccommodate said cable having an initial 10 foot straight section ofconduit, followed by a first 90° bend having a left-orientation,followed by a second 90° bend having a right-orientation, followed by a30 foot straight section of conduit, followed by a third 90° bend havinga right-orientation, followed by a 5 foot straight section of conduit,followed by a fourth 90° bend having a right-orientation, followed by a10 foot straight section of conduit.
 7. In a method for manufacturing apower cable of the type comprising a conductor and an extruded sheathsurrounding at least said conductor, in which the sheath has at leastits exterior portion formed of nylon material, the improvement in whicha silicone based pulling lubricant is introduced in said material inconnection with a process of extrusion of the sheath as one of the stepsfor the overall manufacture of the cable, which lubricant after suchintroduction permeates throughout at least said exterior portion of thesheath, thereby to become available at the exterior surface of saidsheath to facilitate the installation of said cable to be pulled alongan installation surface through building passageways in rafters orjoists or conduit bends, the lubricant being in a concentrationsufficient to reduce the required installation pulling force forinstallation of said cable through said building passageways.
 8. Theprocess as defined by claim 7 in which the silicone based pullinglubricant is high molecular weight silicone oil.
 9. The process asdefined by claim 8 in which the concentration, by weight, of the highmolecular weight silicone oil is at least 9% by weight.
 10. The processas defined by claim 7 in which the concentration, by weight, of thesilicone based pulling lubricant is at least 9% by weight.
 11. Theimprovement as defined by claim 7, wherein the required installationpulling force is quantifiably measureable by a test apparatus as lessthan the required installation pulling force to pull a power cable ofthe same type and size having only externally applied lubricant throughsaid test apparatus, the test apparatus being defined as an initial 10foot straight section of conduit, followed by a first 90° bend having aleft-orientation, followed by a second 90° bend having aright-orientation, followed by a 30 foot straight section of conduit,followed by a third 90° bend having a right-orientation, followed by a 5foot straight section of conduit, followed by a fourth 90° bend having aright-orientation, followed by a 10 foot straight section of conduit.12. The improvement as defined by claim 7 in which the requiredinstallation pulling force is a quantifiable reduction of at least about50% in comparison to the required installation pulling force of anon-lubricated cable of the same cable type and size through anarrangement of conduit, the arrangement of conduit (i) constructed of aPVC conduit that is sized to accommodate said power cable and (ii)comprising a first conduit segment of about 10 feet separated from asecond conduit segment of about 30 feet by two 90° bends, the secondconduit segment separated from a third conduit segment of about 5 feetby a 90° bend, and the third conduit segment separated from a fourthconduit segment of about 10 feet by another 90° bend.
 13. The method asdefined by claim 7 and the manner by which said lubricant is introducedin connection with the sheath extrusion process is by the lubricanthaving been combined with the nylon material to form lubricated nylonmaterial pellets used for the extrusion of the sheath.
 14. The method asdefined by claim 7 in which an extruder is used for the extrusionprocess and the manner by which said lubricant is introduced inconnection with the sheath extrusion process is by injection of both thelubricant and the nylon material directly into the extruder.
 15. Theprocess as defined by claim 7, wherein the so manufactured power cablehas the characteristic that a coefficient of friction of said cable isabout the same or less than a coefficient of friction of another powercable of the same type and size having only externally applied lubricantand substantially no other lubricant, the coefficient of friction beingdeterminable based on a frictional force between a cable and a PVCconduit, said frictional force determinable as a function of an averageback tension applicable to the cable and an average amount of forcerequired to pull the cable through a test apparatus, the test apparatuscomprising (i) PVC conduit that is sized to accommodate the cable, (ii)a first conduit segment of about 30 feet, (iii) a second conduit segmentof about 5 feet and (iv) a third conduit segment of about 10 feet witheach conduit segment separated by a 90° bend, wherein the test apparatusapplies a back tension to the cable.
 16. The process as defined by claim15 wherein the coefficient of friction of the so manufactured powercable is between about 0.125 and about 0.250.
 17. The process as definedby claim 16 wherein the silicone based pulling lubricant resulting insaid coefficient of friction is, respectively, between about 14.00%, byweight, and about 3.00%, by weight.
 18. The process as defined by claim15 wherein the coefficient of friction of the so manufactured powercable is between about 0.125 and about 0.2.
 19. The process as definedby claim 18 wherein the silicon based pulling lubricant is,respectively, between about 14.00%, by weight, and about 5.00%, byweight.
 20. The process as defined by claim 15, wherein the externallyapplied lubricant is one of fluorinated oil and molybdenum disulfide.21. The process as defined by claim 15, wherein the externally appliedlubricant is Y
 77. 22. The process as defined by any one of claims 15and 21, wherein the conduit fill is about 28%.
 23. An improved processof manufacturing a finished power cable assembly of the type comprisinga central conductor and a surrounding sheath of at least one outer layerof nylon material defining the exterior surface of the finished cable,said process comprising: (a) combining a erucamide pulling lubricantwith said nylon material, the erucamide pulling lubricant being of aconcentration sufficient to reduce the required installation pullingforce of the cable during its installation through building passagewaysin rafters or joists or conduit bends, and further of the type whicheither permeates throughout, or migrates through, the at least one outerlayer of the sheath to be available at the said exterior surface as saidcable is pulled along an installation surface; and (b) extruding saidcombined erucamide pulling lubricant and said nylon material to surroundsaid central conductor with at least said outer layer.
 24. The processas defined by claim 23 in which the erucamide pulling lubricant is in aconcentration, by weight, of approximately 0.85%.
 25. The process asdefined by claim 23 in which the erucamide pulling lubricant is in aconcentration, by weight, of between about 0.25% and 0.85%.
 26. In amethod for manufacturing a lubricated power cable of the type comprisinga conductor and an extruded sheath surrounding at least said conductor,in which the sheath has at least its exterior portion formed of nylonmaterial, the improvement in which a pulling lubricant is introduced insaid material in connection with a process for extrusion of the sheath,which pulling lubricant after such introduction becomes available at atleast the exterior surface of said sheath to facilitate such lubricatedcable to be pulled along an installation surface through buildingpassageways in rafters or joists or conduit bends, the lubricant beingin a concentration sufficient to reduce the required installationpulling force, for installation of the lubricated cable through saidbuilding passageways, from an installation pulling force required toinstall, through said passageways, cable of the same type and size, buthaving essentially no lubrication at said exterior portion, wherein therequired installation pulling forces correspond to those which would bemeasured by pulling the said cable through test apparatus incorporatingan arrangement of PVC conduit that is sized to accommodate the cablehaving an initial 10 foot straight section of conduit, followed by a 90°bend having a left-orientation, followed by a first 90° bend having aright-orientation, followed by a 30 foot straight section of conduit,followed by a second 90° bend having a right-orientation, followed by a5 foot straight section of conduit, followed by a third 90° bend havinga right-orientation, followed by a 10 foot straight section of conduit.27. The process as defined by claim 26, wherein the requiredinstallation pulling force for installation of the lubricated powercable through the test apparatus would be reduced between about 25% andabout 75%, from an installation pulling force that would he required toinstall through the test apparatus the cable of the same type and sizeand having essentially no lubrication at said exterior portion.
 28. In amethod for manufacturing a lubricated power cable of the type comprisinga conductor and an extruded sheath surrounding at least said conductor,in which the sheath has at least its exterior portion formed of nylonmaterial, the improvement in which a pulling lubricant is introduced insaid nylon material in connection with a process for extrusion of thesheath, which pulling lubricant after such introduction becomesavailable at at least the exterior surface of said sheath to facilitatesuch lubricated cable to be pulled along an installation surface throughbuilding passageways in rafters or joists or conduit bends, thelubricant being in a concentration sufficient to reduce the requiredinstallation pulling force, for installation of the lubricated cablethrough said building passageways, of a quantifiable reduction of atleast about 50% of the required installation pulling force to install,through said passageways, cable of the same type and size as saidlubricated cable, but having essentially no lubrication at said exteriorportion, wherein the respective required installation pulling forcescorrespond to those which would be measured by pulling the said cablethrough test apparatus incorporating an arrangement of conduit (i)constructed of a PVC conduit that is sized to accommodate said powercable, and (ii) comprising a first conduit segment of about 10 feetseparated from a second conduit segment of about 30 feet by two 90°bends, the second conduit segment separated from a third conduit segmentof about 5 feet by a 90° bend, and the third conduit segment separatedfrom a fourth conduit segment of about 10 feet by another 90° bend. 29.The method of claim 28, wherein the quantifiable reduction is up toabout 75%.
 30. In a method for manufacturing a lubricated power cable ofthe type comprising a conductor and an extruded sheath surrounding atleast said conductor, in which the sheath has at least its exteriorportion formed of nylon material, the improvement in which a pullinglubricant is introduced in said material in connection with a processfor extrusion of the sheath, which lubricant after such introductionbecomes available at at least the exterior surface of said sheath tofacilitate such cable to be pulled along an installation surface throughbuilding passageways in rafters or joists or conduit bends, thelubricant being in a concentration sufficient to reduce the requiredinstallation pulling force, for installation of said lubricated cablethrough said building passageways, a quantifiable reduction of up toabout 75% of the required installation pulling force to install, throughsaid passageways, cable of the same type and size as said lubricatedcable, but having essentially no lubrication at said exterior portion,the respective required installation pulling forces corresponding tothose which would be measured by pulling the said cable through testapparatus incorporating an arrangement of conduit (i) constructed of aPVC conduit that is sized to accommodate said cable, and (ii) comprisinga first conduit segment of about 10 feet separated from a second conduitsegment of about 30 feet by two 90° bends, the second conduit segmentseparated from a third conduit segment of about 5 feet by a 90° bend,and the third conduit segment separated from a fourth conduit segment ofabout 10 feet by another 90° bend.